The present invention relates to a process for forming ballistic flat plate resistant materials comprising glass fibers and polyester resin.
Ballistic resistant articles containing high strength fibers are known to be useful for a variety of military applications. Such fibers in fabric form are encapsulated or embedded in a thermoset resin to form a composite article. Military Specification MIL-L-62474B provides an example of one such laminate or composite employing a polyaramide and a laminating resin which is the cured reaction product of polyvinyl butyral, phenol formaldehyde, and trimethylol phenol and phthalic anhydride. Such laminates, while useful for various armor applications have some drawbacks. One drawback in particular is that these laminates cannot be used to form flat plate ballistic resistant materials without compromising the structural strength of the material.
In order for a composite to be useful for flat plate ballistic resistant applications, it is important that the composite possess a wide balance of properties including satisfactory performance as a ballistic system and meet fire-resistance, smoke-resistance and non-toxicity standards
It is also important that the composite possessing these desirable properties be capable of being manufactured in an efficient manner. Currently, processes for producing flat plate ballistic resistant composites require labor intensive manufacturing operations.
A composite having these properties is identified herein and is formed from woven glass roving made from high strength magnesia aluminosilicate glass fibers and an unsaturated isophthaic-maleic-propylene glycol polyester resin which can be cured to a thermoset condition with a comonomer comprising, for example, styrene, diallyl phthalate or methyl methacrylate, and a free radical catalyst. Resin solutions which are identified herein as producing satisfactory results include a resin system having a low acid number polyester. Due to the properties of the resin system, the manufacturing of such ballistic resistant composites of this type have only previously been possible using a manual hand layup technique. However, this technique is not well adapted for the reliable production of flat plate composites in an expedient commercial and economical manner.
In accordance with the present invention an economical and commercially satisfactory process is provided for manufacturing flat plate composites. Typically the composites can be formed having thickness on the order of at least about 1/16 inch and the process is surprisingly capable of producing high quality composites having thickness of up to and including 3 inches in thickness. According to the present invention, the resin is cured by the use of a polymerizable monomer such as styrene and a free radical initiator. It has not been previously expected that such flat plate composites could be expediently formed since it is known that problems often result due to internal cracking of the composite as a result of the exothermic reaction which occurs during the forming process of the flat plate composites.
It is therefore, an object of this invention to provide a process for the production of flat plate ballistic resistant materials.